The present intention directed to a device for detecting the presence of substances in a fluid sample and more specifically to an assay kit for qualitative and semi-quantitative analysis of fluid sample and a method for manufacturing same.
Devices for testing for the presence of single or multiple substances in a single fluid sample are well known. The demand for inexpensive, accurate and simple to use devices for testing, or assaying, biological specimens has increased in recent years in both medical and non-medical settings. For example, in a hospital where patients are subjected to massive dosages of antibiotics, a small amount of blood may be withdrawn from the patient and the serum assayed for determining an if an appropriate amount of antibiotic is present in the blood. As another example, in a hospital emergency room where an overdose patient has impaired cognitive function, or is a small child unable to communicate, the type of drug overdosed must be quickly determined in order to ensure correct administration of treatment. Nonmedical uses of assaying methods and devices include testing of the general population by employers, government agencies, sports groups and other organizations for employment and maintenance of safety in the workplace. Because of increasingly large numbers of persons being tested, there is a strong need for inexpensive, easy to use and reliable test devices.
Reagent test devices have been developed which generally include an absorbent membrane having incorporated therein a specific reagent which manifests a detectable response, for example a color change, in the presence of a specific component of a sample fluid that is absorbed by the membrane.
Many such test devices for detecting body fluid components are capable of making not only qualitative, but also quantitative or semi-quantitative measurements. Thus, by observing a color change response after a certain period of time, an analyst can obtain not only a positive indication of the presence of a specific component, but also an estimate of how much of the component is present in the sample.
One method for semi-quantitative analysis of a sample involves the uses of tags or marker agents in addition to the component specific reagent. Generally, a known amount of a marker agent is combined with a fluid sample in order to enable the sample component in question to bind with the marker agent, if the component is present in the sample. After the marker agent has become saturated with the component, any uncombined component remaining in the sample, i.e. the portion not bound to the marker, may cause a detectable response in the component specific reagent. Thus, by using known amounts of a marker agent, a relative amount of a sample component can be determined.
Conventionally, many test devices for determining multiple, distinct components of a sample fluid, or for performing semi-quantitative analysis utilize multiple test strips or filaments, each being impregnated or coated with the specific reagent. During assembly of the assaying kit, the separate strips are aligned in a common holder or container. A reservoir in the container is used to hold a fluid sample, and the reservoir and strips are so arranged such that each of the strips will absorb some of the fluid sample.
Although inexpensive materials may be used in the manufacture of conventional assaying devices, such devices require individual alignment and fastening of multiple, separate strips into a holder. The need for handling of a number of individual strips substantially adds to manufacturing time and cost. Moreover, the chance for inaccuracy of test results increases with increased number of strips, as strips may become lost, damaged or misaligned during the assembly process.
The present invention provides a device for testing of multiple substances in a single fluid sample, which is reliable and inexpensive to manufacture because it includes a single, unitary membrane having a number of commonly connected channels with multiple reagents disposed thereon.
The present invention provides an assaying device, and method for making same, which generally comprises a unitary, integral membrane made of a material capable of absorbing a fluid sample, said membrane including a plurality of die cut slots therein which define multiple, commonly connected, absorbent membrane channels.
Assaying means for indicating a presence of at least one component of the fluid sample is provided. The assaying means comprises one or more capture zones, disposed, for example, in a band or stripe fashion across the membrane. Each capture zone includes a particular reagent therein. The reagent may comprise any suitable composition known in the art which will provide a detectable response in the presence of the component in question. For example, the reagent may be a drug conjugate for detecting the presence of an illicit drug in a body fluid sample.
Preferably, the capture zone stripe is disposed on the membrane generally perpendicularly to the die cut slots and channels. As will be discussed in detail hereinafter, the present invention may include a plurality of said capture zones which have been simultaneously striped onto the membrane, each being generally parallel to one another and each containing a reagent for detecting a particular component of the sample.
Alternatively, or in addition to, the multiple capture zones, means for enabling semi-quantitative analysis may be provided such that a relative amount of a component in the sample may be determined. For example, the assaying means may additionally comprise a plurality of marker zones, disposed on an upstream end of the absorbent channels, each marker zone including a different concentration of a particular signal carrying agent. Each channel is then useful for measuring for the presence of a predetermined minimum level of component in the fluid sample.
In the semi-quantitative analysis embodiment, the slots between the channels function in part to prevent mixing of conjugates in one channel with conjugates in an adjacent channel, thus preserving integrity of test results.
Preferably, the slots are die cut into the membrane such that the slots are disposed inside a perimeter of the membrane such that the perimeter is comprised of a continuous common area about the die cut slots.
The present invention preferably includes a rigid holder for containing the unitary membrane and enabling hygienic handling thereof. The holder may be a cassette comprised of a cover portion and a base portion with the base portion including interior projections for engaging the slots and accurately aligning the membrane. The top portion of the cassette includes apertures therein for receiving the fluid sample and windows for enabling observation of capture zones when the membrane is enclosed between the cover and base. In addition, the cassette cover may include grooves for receiving the base projections, thus providing a fluid tight fitting between adjacent channels and preventing shifting or misalignment of the membrane.
The method of the present invention generally includes the steps of striping a continuous membrane ribbon with single or multiple reagents, for example, drug conjugates in the case of drug testing, and die cutting individual unitary membranes, each having multiple channels, therefrom. The die cutting step includes the step of cutting slots into each membrane to define the channels, the slots and channels being disposed perpendicular to the striped reagents. The unitary membrane is inserted into a cassette having interior projections for engaging the slots and aligning the membrane with the windows in the cassette for enabling observation of the capture zones.